This invention relates generally to industrial process control systems having process instruments. More particularly, the present invention relates to industrial process control systems having systems and methods for performing diagnostic evaluations of computational output generated by process control instruments.
Process instruments are used to monitor process variables, such as pressure, temperature, flow and level, of process fluids used in industrial processes. For example, process transmitters are typically employed in industrial manufacturing facilities at multiple locations to monitor a variety of process variables along various production lines. Process transmitters include sensors that produce an electrical output in response to physical changes in the process. For example, pressure transmitters include pressure transducers that produce an electrical output as a function of the pressure of a process fluid, such as in water lines, chemical tanks or the like. Each process transmitter also includes transmitter electronics for receiving and processing the electrical output of the sensor so that the transmitter and process can be monitored locally or remotely. Locally monitored transmitters include displays, such as LCD screens, that show the electrical output at the site of the process transmitter. Remotely monitored transmitters include electronics that transmit the electrical output over a control loop or network to a central monitoring location such as a control room. Configured as such, the process can be regulated from the control room by including automated switches, valves, pumps and other similar components in the process control system and the control loop.
Transmitter electronics also include computational software and hardware such that the magnitude of the sensed process variable can be used to determine a process condition, such as the mass flow rate of the process fluid. As such, transmitter electronics typically include software that performs a computational analysis of the sensed process variable based on user defined process control inputs, such as the fluid type and primary element type. In order to accurately assess the process condition, full computational analysis of the process variable involves complex calculations. The hardware of the transmitter electronics is, however, typically limited in the complexity of the calculations which it can execute. For example, typical process transmitters operate with a very limited power supply, such as what is available from a 4-20 mA system. As such, processors provided within the transmitter electronics typically have fairly low clock speeds, such as 490 kHz, to reduce power demands. It is, therefore, necessary to reduce the complexity of the calculations which the transmitter processors perform so that, for example, computed results can be obtained in a reasonable amount of time. For example, the complex equations are often replaced with more basic algorithm-based calculations, as is explained in greater detail in U.S. Pat. No. 6,182,019 to Wiklund and assigned to Rosemount Inc., Eden Prairie, Minn. The computational analysis performed by the transmitter electronics is typically received at a control room via a control loop with which the process transmitters is on-line. Subsequent evaluation of the algorithm-based computational analysis performed by the transmitter electronics requires user analysis, which typically involves manual computations of the complex equations and the algorithms. There is a need for more expediently evaluating accuracy of process conditions calculated by process transmitter electronics.